Field of the Invention
The present invention relates to liquid crystal display devices.
Description of the Background Art
Electro-optical display devices, or, liquid crystal display devices that employ the in-plane switching (IPS) or the fringe field switching (FFS) in particular need to dissipate electric charge on a display surface of a display panel in order to avoid degradation of display quality. For example, as described in Japanese Patent Application Laid-Open No. 2008-145462, such a device typically includes a conductive tape or conductive paste to electrically connect an electrode located on a TFT substrate with the display surface of the display panel.
The device described in Japanese Patent Application Laid-Open No. 2008-145462 includes, in a terminal area, not only a grounding electrode but also components such as an ID pad, a discrimination mark, a driver IC, and a flexible printed circuit (FPC). Many recent thin-frame display devices have failed to leave sufficient space for a pattern of the grounding electrode, which is to be formed separately from patterns of the above-mentioned components and is to be designed specifically for an electrical connection with a transparent conductive film located on the upper surface of a color filter substrate.
Unlike the conductive paste, the conductive tape for use in establishing an electrical connection between such an electrode and the display surface of the display panel needs to cover a wide area so as to ensure its adherence and allow necessary workspace for its affixation. This structure fails to provide greater flexibility in designing micro-display panels and thin-frame display panels.
To overcome the above-mentioned problem associated with the design requirements, the conductive paste is used to electrically connect such an electrode with the display surface of the display panel, thereby offering a space-saving design. An example of this technique is disclosed in Japanese Patent Application Laid-Open No. 2008-145686.
However, recent liquid crystal display devices have stringent design requirements due to the trend toward thin-frame display devices, and thus, the above technique disclosed in Japanese Patent Application Laid-Open No. 2008-145686 may not meet the requirements.
To overcome the problem associated with the design requirements, another technique has been developed to provide a thin-frame display device in which an inspection pad doubles as the grounding electrode to dissipate electric charge. An example of this technique is disclosed in Japanese Patent Application Laid-Open No. 2014-085424.
Although the display device according to the technique described in Japanese Patent Application Laid-Open No. 2014-085424 includes a switching element located between the inspection pad and a panel display unit (display area), the inspection pad which doubles as the grounding electrode is electrically connected to the panel display unit. In the event of the entry of electric charge associated with static electricity into, for example, the color filter, the conductive paste, or the conductive tape, the electric charge can probably enter the display area through signal lines and accordingly break signal lines and TFT elements located in display pixels.